This invention relates generally to a binocular telescope, and in particular to a pivot-joint construction for a binocular telescope having a collapsible bridge between parallel telescope tubes. In most conventional binocular telescopes or field glasses, either the connecting bridge and the two eyepiece tubes, or at least the connecting bridge, are fabricated from metal. Heretofore, it has not been possible to manufacture a satisfactory binocular telescope entirely from synthetic material. This was due in part to the fact that it was not possible to satisfy the stringent requirements of precision, especially the requirement of parallelism between the axes of the eyepieces when using parts fabricated from synthetic material. Application of known constructions utilized in telescopes fabricated from metallic material did not produce satisfactory results with telescopes fabricated from synthetic material. This has been especially true in connection with double-hinged binocular telescope constructions.
In a conventional pivot-joint construction described in German Patent No. DT-GM-7 247 999 the two adjustable tubes for adjusting the interocular distance between eyepieces are assembled in adjustable form on a connecting bridge. In this construction the required friction between the hinged elements is produced by means of tension elements pre-stressed along the axial direction of the hinge. The necessary friction is produced in the direction of the hinge shaft on two storage holes which are compressed by the metal bridge. The pre-stressing in these conventional constructions occurs by means of a headless screw that is rotatable along the axis of the hinge on which lower part there is assembled a pressure or thrust body with a central receptacle for a ball thrust. This thrust body, like the headless screw, is located in the blind storage hole of the hinge tube. A cone-shaped catch opening is formed in the metal bridge opposite the thrust body. The required friction is insured by adjusting the headless screw which can be tightened or loosened, thereby resulting in a greater or a lesser pressure on the ball in the receptacle. It is questionable whether the required forces can be exerted without causing deformation of the connecting bridge even when the main elements are fabricated from metal. Such deformation has a negative influence on the parallelism of the axes of the eyepieces. Thus, such a construction is wholly unsuitable for use in telescopes wherein the main elements, namely the telescope tubes and the connecting bridge, are fabricated from synthetic materials.
Accordingly, use of such known constructions in a binocular telescope formed from synthetic material would surely lead to deformation of the connecting bridge and/or the storage holes provided in the hinge tabs on the tubes. Such a telescope would not provide a sharp image because of a lack of axes parallelism in the beam paths. Thus, it is desirable to depart from the conventional state of technology relating to metal telescopes and provide a pivot-joint construction for a binocular telescope wherein two adjustable tubes for adjusting the interocular eyepiece distance are pivotally mounted on a connecting bridge which takes into consideration the special requirements of binocular telescopes fabricated from synthetic materials. In addition, it is desirable to provide a construction which insures axes parallelism of the beam paths within the tolerances required.